This invention relates to a mattress construction and particularly to an arrangement for providing greater spring resistance in parts of the mattress and to an upholstery construction for use in construction of mattresses and the like.
One type of mattress is formed substantially from interconnected springs so as to form a spring array of helical coiled springs interconnected in columns and rows with the axis of the spring transverse to the array. The spring array thus provides the resistance to compression width wise of the mattress that is in the direction transverse to the array. The array thus forms a first planar surface on one face and a second planar surface on the opposed face. Over the first and second surfaces are applied firstly a layer of a scrim material which engages the end faces of the springs. On top of the scrim material is provided a resilient layer sometimes a foam and sometimes of a felted cotton material. Outside the resilient layer is applied a quilted outer covering which generally covers both the first and second surfaces and extends around the sides of the array to encase the whole mattress.
As is well known in the art, many different types of materials are used for the individual layers and these can be selected accordingly.
In one type of spring array construction, the individual coil springs are shaped with an end turn of the wire forming the coil spring of larger diameter than the plurality of intermediate turns to form in effect an hour glass shape. This type of coil is known as a BONNEL coil and is widely used in the upholstery art.
These coils are then connected together at the points of contact between each spring and the four adjacent springs in the adjacent columns and rows. Each connection is made by a helical coupling element which is threaded around the adjacent points of the end turns of the springs. Thus each helical coupling element extends across the full width of the mattress and wraps around the adjacent spring of two rows. Each end turn is therefore connected to the end turn of the next adjacent spring by an inextensible wire member which holds the end turns together in a common plane.
Another type of spring construction is called a pocket spring in which each spring is of the simple constant diameter helical type and is received within a fabric pocket. The pockets are then sewn together in the planar array with the fabric pockets holding each spring close to or in contact with its next adjacent springs.
In recent years the trend has been toward an increasing stiffness of the mattress that is an increase in the resistance to compression along the springs. In one example this is achieved by the attachment of elastic straps across the mattress generally in the central third of the mattress which is known to take the majority of the weight of the user when lying on the mattress. A number of the straps are therefore attached across the mattress and have ends attached to the side wires of the mattress so that the elastic straps tend to resist compression of the mattress in this area.
An alternative technique which has been employed is that of inserting rectangular strips of foam material into the space between each spring and the next adjacent spring. Thus the foam material has a width equal to the spacing between the intermediate turns of the coils and a height slightly less than the height of the coils so that it can be received under the end turn and outside the intermediate coils.
This technique has achieved little commercial success and has little technical effect since the resilience of the foam does not significantly add to the spring resistance of the wire springs.
Canadian Patent 449744 discloses an arrangement for assisting a spring of the Bonnel coil type at its position of maximum compression. The patent discloses the provision of a square cross section elongate core which is inserted into the spring and has a length substantially equal to the length of the spring. The dimension of the square cross section is such that the diagonal is slightly greater than the diameter of the intermediate coils of the spring so that the core is compressed at its point of engagement with the intermediate turns and bulges out between the intermediate turns. In the dimension at right angles to the sides of the core, the sides are spaced away from the inside of the spring since that dimension is less than the diameter of the spring. This core is formed of a resilient foam material and is stated to preclude total collapse of the spring and to arrest the action of the spring only when it becomes for the most part fully compressed. This core is therefore used in a situation where the spring is intended to be compressed vigorously for example in a car seat when used by a heavy occupant. The core has little effect at the normal expanded position of the spring and only begins to have its effect when the spring is substantially fully compressed.
In the situation of a mattress of the above type, full compression of the spring almost never occurs. The spring is intended to operate only in a very small range from the fully expanded position to a slightly compressed position. The above patent is therefore of little relevance to the construction of a mattress.
Another arrangement of upholstery construction is shown in a number of patents for example U.S. Pat. No. 3,401,411 (Morrison); U.S. Pat. No. 4,154,786 (Plasse); U.S. Pat. No. 4,862,540 (Savenije); U.S. Pat. No. 5,020,852 (Marion); U.S. Pat. No. 3,145,020 (Calla); Canadian 449,744 (Groom); Canadian 435,149 (Marsack); Canadian 2,013,169 (Reinhardt); Canadian 1,213,381 (Savenije); Canadian 967,294 (Frey). In this construction the mattress or other upholstery element is effectively formed of foam and particularly a subsantially solid block of foam with the foam forming the upper and lower surfaces and providing the majority of the resistance to compression. However the above patents have realized the desirability of embedding spring coils in the foam to assist in the resistance to compression. In some cases a circular cylindrical slot is formed in the foam and a coil inserted into the slot. In other cases the same construction is provided by separate foam pieces including a cylindrical core which is inserted inside the spring. However such a construction is effectively related to manufacture of products from foam with a spring assist and is therefore irrelevant to the above mattress construction using the coupled spring array.